Device including an epitaxial nickel silicide on (100) Si or stable nickel silicide on amorphous Si and a method of fabricating the same

ABSTRACT

An integrated circuit device, and a method of manufacturing the same, comprises an epitaxial nickel silicide on (100) Si, or a stable nickel silicide on amorphous Si, fabricated with a cobalt interlayer. In one embodiment the method comprises depositing a cobalt (Co) interface layer between the Ni and Si layers prior to the silicidation reaction. The cobalt interlayer regulates the flux of the Ni atoms through the cobalt/nickel/silicon alloy layer formed from the reaction of the cobalt interlayer with the nickel and the silicon so that the Ni atoms reach the Si interface at a similar rate, i.e., without any orientation preference, so as to form a uniform layer of nickel silicide. The nickel silicide may be annealed to form a uniform crystalline nickel disilicide. Accordingly, a single crystal nickel silicide on (100) Si or on amorphous Si is achieved wherein the nickel silicide has improved stability and may be utilized in ultra-shallow junction devices.

FIELD OF THE INVENTION

[0001] This invention relates to high performance complementary metaloxide semiconductors (CMOS) and/or very short channel length, ultrashallow source/drain metal oxide semiconductor (MOS) transistors and,more particularly, to an integrated circuit device including anepitaxial nickel silicide on (100) Si or a stable nickel silicide onamorphous Si wherein cobalt is utilized as an interlayer in thefabrication of the silicide, and to a method of manufacturing the same.

BACKGROUND OF THE INVENTION

[0002] Titanium silicide and cobalt silicide are each currently beingused in salicide manufacturing processes to produce metal oxidesemiconductor (MOS) transistors. Titanium silicide has a disadvantage inthat it is difficult to transform the silicide to a low resistivity C54phase when the polysilicon line width is reduced. Cobalt silicide hasthe disadvantage of a high silicon (Si) consumption rate to form cobaltdisicilide. Therefore, it is difficult to apply cobalt silicide directlyon an ultra-shallow source/drain area. Moreover, a reduction in thejunction depth requires a very flat interface between the silicide layerand the silicon active layer.

[0003] Nickel silicide is more suitable for ultra-shallow junctionapplications because nickel monosilicide (NiSi) consumes only 1.83Angstoms (Å) of Si per Å of nickel (Ni) as compared with 3.64 Å of Siper Å of cobalt (Co) needed to form CoSi₂. Moreover, epitaxial silicideis the ideal material for shallow junctions because of the lack of anypreturbation from individual grains, plus the advantages of higherthermal stability and lower resistivity and interfacial stress. However,NiSi is not stable at temperatures higher than 700° C. In particular,the NiSi further reacts with Si to convert to NiSi₂, and at highertemperatures agglomerates to isolate islands within the film. Becausefuture advanced integrated circuit (IC) processes will involve hightemperatures, it is important to establish a method to form a silicideon an ultra-shallow junction which will be stable at temperatures ofabout 800° C. or higher.

[0004] Adding platinum (Pt) to improve the thermal stability of nickelsilicide has been discussed. However, it has been observed thatelectrically active defects in N-type Si were induced by the addition ofPt. The addition of Iridium (Ir) to a nickel silicide has been shown toimprove the stability of the nickel silicide up to temperatures of 850°C. Moreover, good junction integrity in 40 nm ultra-shallow junctionswas demonstrated. However, Iridium has not been used to fabricateepitaxial nickel disilicides because iridium is not easily etchableduring a selective etch process.

[0005] Based on the disadvantages of these prior art silicides, there isa need for a method to form an epitaxial nickel disilicide on (100) Si.It is widely believed that epitaxial silicide will be desirable for usein future devices having very shallow junctions. Epitaxial silicidefilms in general have a very smooth silicide to Si interface. Due to thelack of grain boundaries, these films have high thermal stability andlow resistivity.

[0006] The lattice mismatch between cobalt discilicide and Si is only−1.4%. The lattice mismatch between nickel disilicide and Si is only−0.4%. It is known that single crystal nickel disilicide can be formedon (111) Si by depositing Ni on Si and then annealing the films at ahigh temperature. The interface between the silicide and the (111) Si isvery smooth, as shown in FIG. 1. However, when depositing nickeldisilicide on (100) Si, it has been reported that serious faceting alongthe (111) plane is observed. A schematic of the interface of thesilicide and the (100) Si is shown in FIG. 2.

[0007] A method to avoid the faceting problem in the epitaxial growth ofNiSi₂ on (100) Si has been reported. The method requires theco-deposition of Ni and Si. Selective formation of the silicide,therefore, can not be achieved. Accordingly, it is difficult toimplement this technique to small device fabrication processes.

[0008] Accordingly, there is a need for a method to form single-crystalNiSi₂ on (100) Si that is applicable to standard selective silicideprocesses for fabrication of devices having very small device features.

SUMMARY OF THE INVENTION

[0009] The present invention provides an integrated circuit deviceincluding an epitaxial nickel silicide on (100) Si, or a stable nickelsilicide on amorphous Si, and a method of manufacturing the same. Inparticular, the method comprises depositing a cobalt (Co) interfacelayer between the Ni and Si layers prior to the silicidation reaction.The cobalt/nickel/silicon alloy film formed from the reaction of thecobalt interlayer with the nickel and silicon regulates the flux of theNi atoms through the interlayer so that the Ni atoms reach the Siinterface at a similar rate, i.e., without any orientation preference,so as to form a uniform layer of nickel silicide. Accordingly, a singlecrystal nickel silicide on (100) Si or on amorphous Si is achievedwherein the nickel silicide has improved stability and may be utilizedin ultra-shallow junction devices.

[0010] Accordingly, an object of the present invention is to provide asingle-crystal NiSi₂ on (100) Si without the formation of silicidefaceting along the (111) plane into the Si substrate.

[0011] Another object of the present invention is to provide a nickelsilicide fabrication process that is compatible with proposed future ICfabrication processes, allows selective formation of the silicide, andis inexpensive and simple to conduct.

[0012] Yet another object of the present invention is to provide anickel silicide film for use in ultra-shallow junctions having ajunction depth less than 40 nm, while maintaining the junction integrityand stability of the silicide layer at temperatures above 800° C.,wherein cobalt is incorporated into the silicide layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic of a prior art single crystal nickeldisilicide film grown on (111) silicon, having a smooth nickel-siliconinterface.

[0014]FIG. 2 is a schematic of a prior art single crystal nickeldisilicide film grown on (100) silicon, showing faceting along the (111)plane.

[0015]FIG. 3 is a schematic of nickel atoms of the prior art diffusingalong the (111) plane of a silicon substrate, thereby causing facetformation.

[0016]FIG. 4 is a schematic of nickel atoms diffusing through acobalt/nickel/silicon alloy film formed from the reaction of the cobaltinterlayer with nickel and silicon of the present invention on a (100)silicon substrate, thereby causing uniform growth of a single crystalnickel silicide on the silicon substrate.

[0017]FIG. 5 shows a high resolution X-ray diffraction pattern of anickel silicide film with cobalt addition after annealing at 600° C. forsixty seconds.

[0018]FIG. 6 shows a high resolution X-ray diffraction pattern of anickel silicide film with cobalt addition after annealing at 700° C. forsixty seconds.

[0019]FIG. 7 shows a high resolution X-ray diffraction pattern of anickel silicide film with cobalt addition after annealing at 850° C. forsixty seconds.

[0020]FIG. 8 shows a sheet resistance of a nickel silicide formed from aprior art nickel film wherein the sheet resistance increases attemperatures greater than approximately 600° C.

[0021]FIG. 9 shows a sheet resistance of a nickel silicide formed from anickel film with cobalt at the nickel-silicon interface wherein thesheet resistance decreases with annealing temperature.

[0022]FIG. 10 shows a sheet resistance of a nickel silicide formed froma nickel film having a cobalt layer sandwiched between two nickel layerswherein the sheet resistance decreases with annealing temperature.

[0023]FIG. 11 shows sheet resistance changes with annealing temperaturefor prior art nickel films deposited on amorphous silicon without acobalt interlayer.

[0024]FIG. 12 shows silicide sheet resistance changes with annealingtemperature for a film comprising cobalt sandwiched between two nickelfilms on amorphous silicon.

[0025]FIG. 13 shows silicide sheet resistance changes with annealingtemperature for a film comprising cobalt at the nickel-silicon interfaceon amorphous silicon.

[0026]FIG. 14 shows reverse bias junction leakage measured on prior artultra-shallow junctions after nickel silicide formation without a cobaltinterlayer for N+/P junctions wherein an increase in current with risingannealing temperatures is observed.

[0027]FIG. 15 shows prior art reverse bias junction leakage measured onultra-shallow junctions after nickel silicide formation without a cobaltinterlayer for P+/N junctions wherein an increase in current with risingannealing temperatures is observed.

[0028]FIG. 16 shows reverse bias junction leakage measured onultra-shallow N+/P junctions wherein the nickel silicide was formed fromsequentially deposited cobalt and nickel films, and wherein the filmshows low leakage up to 850° C.

[0029]FIG. 17 shows reverse bias junction leakage measured onultra-shallow P+/N junctions wherein the nickel silicide was formed fromsequentially deposited cobalt and nickel films, and wherein the filmshows decreased leakage compared to prior art nickel silicide filmsformed without a cobalt interlayer.

[0030]FIG. 18 is a flowchart of the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Referring now to the figures, FIG. 1 is a schematic of a priorart single crystal nickel disilicide film grown on (111) silicon, havinga smooth interface.

[0032]FIG. 2 is a schematic of a prior art single crystal nickeldisilicide film grown on (100) silicon, showing faceting along the (111)plane.

[0033] The present invention provides a method of fabricating epitaxialnickel disilicide (NiSi₂) having a smooth silicide/Si interface onamorphous or (100) Si. The invention comprises adding cobalt at theinterface between the nickel (Ni) and the silicon (Si) before thesilicidation reaction. In this manner, single crystal nickel silicide isachieved. The method provides for improved stability of the nickelsilicide over prior art silicide films, and facilitates the fabricationof ultra-shallow junctions, i.e., junctions having a depth of 40 nm orless.

[0034] Applicants believe that the faceting at the silicide/siliconinterface is controlled by kinetics, not thermodynamics. Therefore,Applicants believe that a smooth interface can be generated byregulating the diffusion of Ni atoms and the nucleation and growth ofthe NiSi₂ phase. In particular, the method of the present inventioncomprises adding an interlayer to regulate the flux of the Ni atomstherethrough. The interlayer facilitates the Ni atoms reaching the Siinterface at a uniform rate and reacting with the Si at a uniform rateto form a uniform layer of nickel silicide. This is explained in FIGS. 3and 4.

[0035]FIG. 3 is a schematic of nickel atoms of the prior art diffusedalong the (111) plane of a silicon substrate, i.e., at an acute anglewith respect to the planar surface of silicon substrate 16, therebycausing faceting formation. In particular, the nickel atoms 10 diffusealong the (111) plane 12 and cause the formation of faceting 14 insilicon substrate 16.

[0036]FIG. 4 is a schematic of nickel atoms 10 diffusing through theinterlayer 18 of the present invention on a (100) silicon substrate 16,thereby causing uniform growth of a single crystal nickel silicide 20 onthe silicon substrate. The nickel atoms diffuse through thecobalt/nickel/silicon alloy film formed from the reaction of the cobaltinterlayer with the nickel and the silicon, and reach the siliconinterface without any preference, i.e, without any predeterminedorientation. In other words, the nickel atoms diffuse in a direction 22that is perpendicular to the planar surface 24 of silicon substrate 16.This causes the uniform growth of the single crystal nickel silicide 20.The fabrication steps to form the device shown in FIG. 4 will bedescribed in more detail below.

[0037] In order to confirm the single crystal formation, Applicantsperformed high-resolution x-ray diffraction work on Co-doped nickelsilicide films. The result showed the formation of very high qualitysingle-crystal films, which were strained with respect to the singlecrystal Si substrate.

[0038]FIG. 5 shows a high resolution X-ray diffraction (HRXRD) patternof a nickel silicide film with cobalt addition after annealing at 600°C. for sixty seconds. The ordinate represents counts/second and theabscissa represents 2Theta. The deposited film comprised a cobalt layeron the silicon substrate, wherein the thickness of the cobalt layer wasapproximately 14 Å. A nickel layer having a thickness of approximately69 Å was deposited on the cobalt layer. These two layers were thensubject to annealing at 600° C. for sixty seconds to form the nickelsilicide film. As shown in the HRXRD pattern, a dislicide phase wasformed at 600° C.

[0039]FIG. 6 shows a high resolution X-ray diffraction pattern of anickel silicide film with cobalt addition after annealing at 700° C. forsixty seconds. The ordinate represents counts/second and the abscissarepresents 2Theta. The deposited film comprised a cobalt layer on thesilicon substrate, wherein the thickness of the cobalt layer was 16 Å. Anickel layer having a thickness of 69 Å was deposited on the cobaltlayer. These two layers were then subject to annealing at 700° C. forsixty seconds to form the nickel silicide film. As shown in the HRXRDpattern, the nickel silicide film shows good film crystalline propertiesafter annealing at 700° C.

[0040]FIG. 7 shows a high resolution X-ray diffraction pattern of anickel silicide film with cobalt addition after annealing at 850° C. forsixty seconds. In FIG. 7, the ordinate represents counts/second and theabscissa represents 2Theta. The deposited film comprised a cobalt layeron the silicon substrate, wherein the thickness of the cobalt layer was16 Å. A nickel layer having a thickness of 69 Å was deposited on thecobalt layer. These two layers were then subject to annealing at 850° C.for sixty seconds to form the nickel silicide film. As shown in theHRXRD pattern, the nickel silicide film shows improved film crystallineproperties over prior art films for annealing temperatures greater than700° C. In particular, the figure shows that the disilicide is of highquality and the interface between the silicide and the Si is relativelysmooth. At lower annealing temperatures single crystal films were alsodetected, as shown in FIGS. 5 and 6. However, the film crystallineproperties of those films are not as high as the properties of the filmshown in FIG. 7. In particular, the peak at a 2Theta of approximately 70is approximately 4,000 counts per second in FIG. 5, approximately 10,000counts per second in FIG. 6, and approximately 30,000 counts per secondin FIG. 7.

[0041] Further X-ray diffraction results show that in order to provide adevice having improved crystalline quality, the cobalt interlayerpreferably is provided at the nickel-silicon interface. In anotherembodiment, the cobalt may be provided within the nickel film itself. Ifthe Co is positioned in the middle of the Ni film, Applicants have foundthat the crystalline quality is not as good as in films where the cobaltis deposited at the silicon interface, but such films still haveimproved crystalline quality compared to prior art nickel silicide filmsfabricated without a cobalt interlayer. In particular, these results aredemonstrated by the following figures showing the silicide sheetresistance change with annealing temperature.

[0042]FIG. 8 shows the sheet resistance of a nickel silicide formed froma prior art nickel film, fabricated without a cobalt interlayer, whereinthe sheet resistance increases at annealing temperatures greater thanapproximately 600° C. The silicide was formed from a nickel film havinga thickness of 85 Å, positioned on the silicon substrate. In this figurethe ordinate represents the sheet resistance in ohm/square and theabscissa represents the rapid thermal annealing (RTA) temperature indegrees Celsius.

[0043]FIG. 9 shows the sheet resistance of a nickel silicide filmfabricated from a nickel film with cobalt positioned at thenickel-silicon interface wherein the sheet resistance decreases with theanneal temperature. The silicide was formed from a cobalt film having athickness of 14 Å deposited on the silicon substrate, and a nickel filmhaving a thickness of 69 Å subsequently deposited on the cobalt film.The films were then subjected to annealing. The thermal stability ofthis device is improved over the prior art. In particular, the sheetresistance decreases with annealing temperatures of approximately 400°C. or greater, and remains low at annealing temperatures of 850° C. andgreater. In this figure the ordinate represents the sheet resistance inohm/square and the abscissa represents the rapid thermal annealing (RTA)temperature in degrees Celsius.

[0044]FIG. 10 shows the sheet resistance of a nickel silicide filmfabricated from a cobalt layer sandwiched between two nickel layerswherein the sheet resistance decreases with the anneal temperature. Thesilicide was formed from a first nickel film having a thickness ofapproximately 40 Å deposited on the silicon substrate, a cobalt filmhaving a thickness of 16 Å deposited on the first nickel film, and asecond nickel film having a thickness of approximately 29 Å deposited onthe silicon substrate. The films were then subjected to annealing forapproximately sixty seconds. The thermal stability of this film is alsoimproved over the prior art. In particular, the sheet resistancedecreases with annealing temperatures of approximately 500° C. orgreater, and remains low at annealing temperatures of 850° C. andgreater. In this figure the ordinate represents the sheet resistance inohm/square and the abscissa represents the rapid thermal annealing (RTA)temperature in degrees Celsius. Adding cobalt in the middle of thenickel film improves the film stability, but does not appear to improvethe film's crystallinity. Accordingly, a cobalt film positioned at thesilicon interface is the preferred method of the present invention.

[0045] The present invention provides a nickel silicide, and a method offabricating the same, that is applicable to and stable for use onamorphous silicon. In FIGS. 11 through 13 the amorphous Si was depositedon a thermal oxide by low pressure chemical vapor deposition (LPCVD).The results show that the thermal stability of prior art nickelsilicides on amorphous Si, without the use of a cobalt interlayer duringfabrication, is very poor. In particular, a significant increase insheet resistance is detected even at annealing temperatures of 600° C.However, thermal stability of nickel silicides is much improved with theaddition of a cobalt interlayer of the present invention.

[0046]FIG. 11 shows sheet resistance changes with annealing temperaturefor prior art nickel films deposited on amorphous silicon without acobalt interlayer. A significant increase in the sheet resistance isdetected at temperatures of approximately 600° C. and greater. In thisfigure the ordinate represents the sheet resistance in ohm/square andthe abscissa represents the rapid thermal annealing (RTA) temperature indegrees Celsius.

[0047]FIG. 12 shows silicide sheet resistance changes with annealtemperature for a film comprising cobalt sandwiched between two nickelfilms. A decrease in the sheet resistance is detected at temperatures ofapproximately 600° C. and greater. Moreover, the sheet resistancedetected, on the order of 12 ohm/square, is much lower than the sheetresistances of approximately 100 ohm/square as shown in FIG. 11 for theprior art silicide films. In FIG. 12 the ordinate represents the sheetresistance in ohm/square and the abscissa represents the rapid thermalannealing (RTA) temperature in degrees Celsius.

[0048]FIG. 13 shows silicide sheet resistance changes with annealtemperature for a film comprising cobalt positioned at the nickelsilicon interface on amorphous silicon. A decrease in the sheetresistance is detected at temperatures of approximately 600° C. andgreater. Moreover, the sheet resistance detected, on the order of 12ohm/square, is much lower than the sheet resistance of approximately 100ohm/square as shown in FIG. 11 for the prior art silicide films. In thisfigure the ordinate represents the sheet resistance in ohm/square andthe abscissa represents the rapid thermal annealing (RTA) temperature indegrees Celsius.

[0049] The nickel silicide film of the present invention, and the methodof fabricating the same, is applicable for use in ultra-shallowjunctions. Ultra-shallow junctions, having a junction depth ofapproximately 40 nm or less, were formed by a plasma doping technique.N+/P junctions were formed using a gas mixture of PH₃/He. P+/N junctionswere formed using a gas mixture of B₂H₆/He. Activation was achieved by atwo-step RTA anneal where recrystallization was performed atapproximately 800° C., followed by a spike anneal at approximately 1050°C. The junction depths, as determined by secondary ion mass spectrometry(SIMS) were about 40 nm. Nickel and cobalt were deposited by sequentiale-beam evaporation. The thickness of the Co film deposited was in therange of 14 Å to 20 Å. The Ni film thickness was in the range of 25 Å to130 Å. The silicide was then formed by a RTA anneal, typically at 550°C. The distributions shown in FIGS. 14 to 17 are reverse bias junctionleakages measured on ultra-shallow junctions after silicide formation in100 μm×100 82 m areas at |3V|.

[0050]FIG. 14 shows prior art reverse bias junction leakagedistributions measured on ultra-shallow junctions after nickel silicideformation for N+/P diode junctions wherein an increase in current withrising annealing temperatures is observed. The silicide was formed froma nickel film having a thickness of approximately 68 Å. The RTA step wasperformed consecutively at 550° C., 650° C., 750° C., 800° C. and 850°C., each for 60 seconds. Significant increases in the current with theRTA temperature are observed.

[0051]FIG. 15 shows prior art reverse bias junction leakagedistributions measured on ultra-shallow junctions after nickel silicideformation for P+/N diode junctions wherein an increase in current withrising annealing temperatures is observed. The silicide was formed froma nickel film having a thickness of approximately 68 Å. The RTA step wasperformed consecutively at 550° C., 650° C., 750° C., 800° C. and 850°C., each for 60 seconds. Significant increases in the current with theRTA temperature are observed.

[0052]FIG. 16 shows reverse bias junction leakage measured onultra-shallow N+/P junctions wherein the nickel silicide was formed fromsequentially deposited cobalt and nickel films on a silicon substrate,and wherein the film shows low leakage up to 850° C. The cobalt film hada thickness of approximately 14 to 16 Å and was deposited at the siliconinterface. The Ni film thickness was approximately 69 Å, and wasdeposited on the cobalt film. The device was then annealed. The RTA stepwas performed consecutively at 550° C., 650° C., 750° C., 800° C. and850° C., each for 60 seconds. The sheet resistance remained under about9 ohm/square even after a 30 min anneal at 850° C. The sheet resistanceshowed gradual rising values but there is a three order of magnitudeimprovement from the prior art devices manufactured with silicide andnickel only, and without a cobalt interlayer.

[0053]FIG. 17 shows reverse bias junction leakage measured onultra-shallow P+/N junctions wherein the nickel silicide was formed fromsequentially deposited cobalt and nickel films, and wherein the filmshows decreased leakage compared to prior art nickel silicide films. Thecobalt film had a thickness of approximately 14 to 16 Å and wasdeposited at the silicon interface. The Ni film thickness wasapproximately 69 Å, and was deposited on the cobalt film. The films werethen annealed. The RTA step was performed consecutively at 550° C., 650°C., 750° C., 800° C. and 850° C., each for 60 seconds. The sheetresistance remained under about 9 ohm/square even after a 30 min annealat 850° C. Low leakage was demonstrated for the P+/N junctions up toapproximately 850° C.

[0054]FIG. 18 is a flowchart of the fabrication method of the presentinvention. In particular, step 28 comprises providing a siliconsubstrate. The silicon substrate may comprise an amorphous siliconsubstrate or a (100) oriented silicon substrate.

[0055] Step 30 comprises depositing cobalt and nickel on the amorphoussilicon or on the (100) silicon substrate. In one embodiment, depositionof the nickel and the cobalt comprises depositing a Co film and a Nifilm on the source, drain and polysilicon areas of a device by physicalvapor deposition including sputtering and evaporation, or by chemicalvapor deposition including metalorganic chemical vapor deposition. Inparticular, in this embodiment, step 30 comprises depositing a Co filmon the silicon and then depositing a Ni film on the cobalt film. Thethickness of the cobalt layer typically is in a range of 5 to 20 Å. Thethickness of the Ni layer typically is in the range of 50 to 200 Å. Inanother embodiment, deposition of the cobalt and the nickel may compriseco-sputtering or co-evaporation of the cobalt and the nickel, orsputtering from a Ni—Co target, to form a Co—Ni film. The atomicpercentage of the Co in the Ni typically is in the range of 2% to 15%.In yet another embodiment, step 30 comprises creating a sandwichstructure with a layer of Co in the middle of two Ni layers. In thisembodiment, a first nickel layer is deposited on the silicon, a cobaltlayer is deposited on the first nickel layer, and a second nickel layeris deposited on the cobalt layer. In one example of this embodiment, afirst nickel layer having a thickness of approximately 40 Å is depositedon the silicon substrate, a cobalt film having a thickness of 16 Å isdeposited on the first nickel film, and a second nickel film having athickness of approximately 29 Å is deposited on the silicon substrate.

[0056] Step 32 comprises silicidation of the cobalt and nickel on thesilicon layer. The silicidation step typically is performed in an inertambient or nitrogen ambient, at a temperature in the range of 300° C. to900° C. for a period of 10 sec to two minutes. Single-crystal nickeldisilicide on the amorphous or (100) silicon, with very good crystalperfection, can be achieved at 850° C. This step results in a nickelsilicide layer having cobalt incorporated therein. In other words, thenickel disilicide and the cobalt disilicide are miscible. Both thenickel disilicide and the cobalt disilicide have similar crystalstructures so that the two disilicides from a high quality crystal on(100) silicon. The nickel silicide layer formed typically has athickness in a range of 90 to 700 Angstroms and a cobalt atomicpercentage in a range of two to fifteen percent.

[0057] The method of the present invention typically comprises a rapidthermal anneal step conducted at a temperature in a range of 300 to 700degrees Celsius for a time period in a range of ten seconds to twominutes. When the rapid thermal anneal step is conducted at atemperature lower than 600 degrees Celsius, than a second annealing stepto anneal the silicide film is conducted. The second annealing step,which typically is conducted after etching of the film in a Piranhasolution, is conducted at a temperature of at least 600 degrees Celsiusfor a time period in a range of ten seconds to two minutes.

[0058] Step 34 comprises conducting a selective etch, typicallyconducted in a Piranha solution which consists of sulfuric acid andhydrogen peroxide. The etch temperature typically is between 75° C. and150° C.

[0059] A specific example of one process is given below. First, apre-metal dip of a wafer in a dilute buffered HF solution is conductedfor 20 seconds. Second, the wafer is rinsed in de-ionized water and spundry before being loaded into an e-beam evaporation chamber. The waferused is a patternless p-type (100) silicon wafer. Third, a 15 Å thick Cofilm is deposited by evaporation or sputtering on the wafer. Fourth, a75 Å thick Ni film is deposited by evaporation or sputtering on thecobalt film. Fifth, a RTA anneal in Argon is conducted on the waferincluding the nickel and cobalt films, at 350 to 500° C. for 60 secondsto form a nickel silicide on the wafer, having cobalt complexed therein.Sixth, a selective etch in a Piranha solution is performed on the nickelsilicide formed on the wafer. Seventh, the wafer is subjected to furtherannealing at 600 to 850° C. to convert the nickel silicide tosingle-crystal nickel disilicide with good crystal perfection. The sheetresistance is determined by use of a four-point probe. The filmstructure is analyzed by use of a Phillips Analytical x-ray diffractionsystem in a high resolution mode and by cross-sectional transmissionelectron miscroscopy. The layer composition is analyzed by Rutherfordbackscattering analysis.

[0060] In summary, a significant improvement in the thermal stability ofnickel silicide is achieved by adding cobalt at the nickel/siliconinterface. This process appears to be very useful for the fabrication ofproposed future devices having ultra-shallow junctions. The reason forthe improved thermal stability and low junction leakage is due to anultra-smooth interface, demonstrated by high resolution X-raydiffraction.

[0061] Thus, a method of producing an improved nickel silicide device,and a device incorporating the same, has been disclosed. Althoughpreferred structures and methods of fabricating the device have beendisclosed, it should be appreciated that further variations andmodifications may be made thereto without departing from the scope ofthe invention as defined in the appended claims.

I claim:
 1. A method of fabricating a nickel silicide on a siliconsubstrate, comprising the steps of: providing a silicon substrate;depositing cobalt on said silicon substrate; depositing nickel on saidsilicon substrate, wherein said nickel is in contact with said cobalt;and annealing said cobalt and said nickel to form a nickel silicide onsaid silicon substrate.
 2. The method of claim 1 wherein said step ofdepositing cobalt on said silicon substrate comprises depositing acobalt film directly on said silicon substrate, and wherein said step ofdepositing nickel on said silicon substrate comprises depositing anickel film on said cobalt film.
 3. The method of claim 1 wherein saidstep of depositing nickel on said silicon substrate comprises depositinga first nickel film on said silicon substrate, wherein said step ofdepositing cobalt on said silicon substrate comprises depositing acobalt film on said first nickel film, and wherein said step ofdepositing nickel on said silicon substrate further comprises depositinga second nickel film on said cobalt film to form a nickel-cobalt-nickellayered structure on said silicon substrate.
 4. The method of claim 1wherein said step of depositing nickel on said silicon substrate andsaid step of depositing cobalt on said silicon substrate compriseco-depositing cobalt and nickel on said silicon substrate simultaneouslyto form a nickel-cobalt film on said silicon substrate.
 5. The method ofclaim 2 wherein said cobalt film has a thickness in a range of 5 to 20Angstroms, and said nickel film has thickness in a range of 25 to 200Angstroms.
 6. The method of claim 3 wherein said first nickel film has athickness in a range of of 25 to 200 Angstroms, said cobalt film has athickness in a range of 5 to 20 Angstroms, and said second nickel filmhas thickness in a range of 25 to 200 Angstroms.
 7. The method of claim4 wherein said nickel-cobalt film comprises a cobalt atomic percentagein a range of two to fifteen percent.
 8. The method of claim 1 whereinsaid step of annealing said cobalt and said nickel comprises a firstannealing step conducted at a temperature in a range of 300 to 700degrees Celsius for a time period in a range of ten seconds to twominutes, and wherein when said first annealing step is conducted at atemperature lower than 600 degrees Celsius, then said step of annealingsaid cobalt and said nickel further comprises a second annealing stepconducted at a temperature of at least 600 degrees Celsius for a timeperiod in a range of ten seconds to two minutes.
 9. The method of claim8 wherein said silicidation anneal step converts said nickel silicide tosingle-crystal nickel disilicide having an absence of faceting along a(111) plane into said silicon substrate.
 10. The method of claim 1wherein said silicon substrate is chosen from the group consisting of anamorphous silicon substrate and a (100) silicon substrate.
 11. Themethod of claim 1 wherein said silicon substrate comprises a junctionhaving a depth of at most 40 nm.
 12. The method of claim 1 wherein saidcobalt defines a cobalt interlayer positioned between at least a portionof said nickel and said silicon substrate such that during said step ofannealing said cobalt and said nickel to form a nickel silicide on saidsilicon substrate, said at least a portion of said nickel diffusesthrough said cobalt interlayer.
 13. A microelectronic device comprising:a silicon substrate; and a nickel silicide positioned on said siliconsubstrate, wherein said nickel silicide includes cobalt therein.
 14. Thedevice of claim 13 wherein said device is a junction chosen from thegroup consisting of a P+/N junction and a N+/P junction.
 15. The deviceof claim 13 wherein said device has a sheet resistance of no more thannine ohm/square, as measured across an area of 100 μm×100 μm at |3V|,after annealing of the device for at least thirty minutes at atemperature of at least 600 degrees Celsius.
 16. The device of claim 13wherein said nickel silicide has a thickness in a range of 90 to 700Angstroms, and wherein said cobalt comprises a cobalt atomic percentagein a range of two to fifteen percent in said nickel silicide.
 17. Thedevice of claim 13 wherein said nickel silicide is stable attemperatures greater than 700 degrees Celsius.
 18. The device of claim13 wherein said nickel silicide comprises single-crystal nickeldisilicide having an absence of faceting along a (111) plane into saidsilicon substrate.
 19. The device of claim 13 wherein said siliconsubstrate is chosen from the group consisting of an amorphous siliconsubstrate and a (100) silicon substrate.
 20. The device of claim 14wherein said junction has a depth of at most 100 nm.